Laser welding is commonly used to join plastic or resinous parts, such as thermoplastic parts, at a welding zone. An example of such use of lasers can be found in U.S. Pat. No. 4,636,609, which is expressly incorporated herein by reference.
As is well known, lasers provide a semi-focused beam of electromagnetic radiation at a specified frequency (i.e., coherent monochromatic radiation). There are a number of types of lasers available; however, infrared lasers or non-coherent sources provide a relatively economical source of radiative energy for use in heating a welding zone. One particular example of infrared welding is known as Through-Transmission Infrared (TTIr) Welding. TTIr welding employs an infrared laser capable of producing infrared radiation that is directed by lenses, diffractive optics, fiber optics, waveguides, lightpipes, or lightguides through a first plastic part and into a second plastic part. This first plastic part is often referred to as the transmissive piece, since it generally permits the laser beam from the laser to pass therethrough. However, the second plastic part is often referred to as absorptive piece, since this piece generally absorbs the radiative energy of the laser beam to produce heat in the welding zone. This heat in the welding zone causes the transmissive piece and the absorptive piece to be melted and, with intimate contact, welded together.
Often times, multiple laser beams produced from multiple laser and optical bundle assemblies may be used to weld a single zone. That is, in simultaneous plunge welding, multiple laser sources are used to simultaneously produce a single weld at a specific weld zone. The laser beam from each of the multiple laser sources is delivered to the weld zone by an individual fiber optic bundle, lightguide, and or waveguide (hereinafter collectively referred to an optical bundle). It should be understood that each specific laser source and bundle assembly produces a unique laser output intensity that is a byproduct of the unique characteristics of the laser source and bundles used.
It is frequently desirable to interchange various bundles with different laser sources to produce a desired effect. However, as one skilled in the art will recognize, interchanging a bundle with a different laser source will again produce a unique combination have a different laser output. Typically, it is required that this new combination of laser source and bundle be recalibrated so the exact laser output intensity is known so as to avoid undesired welds. Thus, it is desirable to be able to readily swap bundles with individual laser sources without having to recalibrate each bundle to each laser. This would permit quick and simplified tooling modifications, without the need for costly down time.
It is known to use a single optical sensor positioned near the laser source to provide output energy information. However, this output energy information is only useful when calibrated relative to the laser and bundle being used. Therefore, with a single sensor arrangement, the laser source and bundle assembly still require lengthy delays during calibration.
If one chooses not to calibrate the laser source and bundle assembly, excessive statistical error is introduced. As seen in FIG. 1, when one uses a single optical sensor positioned near the laser source and swaps between bundles, the standard deviation of the raw feedback signal without a calibration factor has been found to be about 57%, as shown in FIG. 1. Obviously, for most applications, this standard deviation is unacceptable. As mentioned above, this deviation could be eliminated by calibration of each laser source and bundle combination. But given the number of interchangeable bundles between various laser sources and machines in a typical commercial application, it is not practical to calculate the calibration factor for every possible combination.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.